1. Field of the Invention
This invention relates to an electrophotographic photosensitive material. More particularly, it relates to an electrophotographic photosensitive material comprising a photosensitive layer containing an organic photoconductor and a polymeric binder.
2. Description of the Art
Organic photoconductors are advantageous over inorganic photoconductors in that they are light in weight, possess good flexibility, provide photosensitive layers excellent in transparency and can easily be combined into a composite material with other materials. Polyvinyl carbazoles, oxadiazoles and pyrazoline derivatives are known as such organic photoconductors.
Basic properties required for electrophotographic photosensitive materials are high static charge acceptance and high charge retentivity in the dark, a high sensitivity, a low residual voltage, a broad spectral sensitivity in the visible region, a high durability, no toxicity, and good processabilities (including a good film-forming property, a high transparency, a high flexibility and a good adaptability to the mass production). Organic photoconductors and inorganic photoconductors, which are satisfactory in all of these basic properties when they are used alone, have not heretofore been proposed. Thus, photoconductors popularly used at present have some defects or others.
Under this circumstance, function-separated electrophotographic photosensitive materials have recently been proposed. These photosensitive materials are based on the concept that the photosensitive layer is divided into layers differing in the function, that is, a charge generating layer for generating charges on absorption of light and a charge transport layer for transporting the formed charges, whereby the range for the selection of materials is broadened and some or all of the basic properties required for electrophotographic photosensitive materials are sufficiently manifested. Many function-separated electrophotographic photosensitive materials have heretofore been proposed, but only a limited number of them have been put into practical use. The practically used photosensitive materials still have some defects or others.
The combination of a charge generating material and a charge transport material has not theoretically been examined, but various combinations have been examined according to trial-and-error procedures.
The U.S. Pat. to Matsumura et al No. 4,463,077 discloses an electrophotographic photosensitive material having an organic photoconductor based upon the &gt;C.dbd.N--N&lt; structure and which differs sharply from the organic photoconductors disclosed and claimed herein.